Qt core and most libraries are written by the same group of people in the same development process. Splitting it up into libraries is good engineering practice

Qt core and most libraries are written by the same group of people in the same development process. Splitting it up into libraries is good engineering practice as it ensures boundaries. (Whether it is packaged into their own dll/so/a/dynlib is a deployment question, you can compile all parts statically together) The licensing is a political/business question independent from code being nice, good and clean. (Except one has to be careful during refactorings, as code might change license, but since afaik the Qt Company has CLAs ensuring copyright ownership they are able to do that)